As long as they have a system in place to which you can pay to put any toon on any server I highly doubt you will ever see another server merge.
Not saying I'm against it though.
Well I suppose that the only drawback would be unlike UR if you pop it below say 30% chances are it's not going to prevent/delay your death as there are plenty of hard hitting weapon based abilities including all executes.
Only thing I can think of.